1. Field of the Invention
The invention relates generally to concrete finishing trowels and, more particularly, to riding concrete finishing trowels having power steering systems.
2. Description of the Related Art
A variety of machines are available for smoothing net and partially cured concrete. These machines range from simple hand trowels, to walk-behind trowels, to self-propelled riding trowels. Regardless of the mode of operation of such trowels, the powered trowels generally include one or more rotors that rotate relative to the concrete surface. Riding finishing trowels can generally finish large sections of concrete more rapidly and efficiently than manually pushed or guided hand-held or walk behind finishing trowels.
Riding concrete finishing trowels typically include a frame having a cage that generally encloses two, and sometimes three or more, rotor assemblies. Each rotor assembly includes a driven vertical shaft and a plurality of trowel blades mounted on and extending radially outwardly from the bottom end of the driven shaft. The driven shafts of the rotor assemblies are driven by one or more engines mounted on the frame and typically linked to the driven shafts by gearboxes of the respective rotor assemblies.
The weight of the finishing trowel, including the operator, is transmitted frictionally to the concrete surface by the rotating blades, thereby smoothing the concrete surface. The pitch of individual blades can be altered relative to the driven shafts via operation of a lever and/or linkage system during use of the machine. Such a construction allows the operator to adjust blade pitch during operation of the power trowel. As commonly understood, blade pitch adjustment alters the pressure applied to the surface being finished by the machine by altering the contact surface area of the blades.
The rotor assemblies of riding trowels also can be tilted relative to the vertical axis of the driven shaft for steering purposes. By tilting the rotor assemblies, the operator can utilize the frictional forces imposed on the blades by the concrete surface to propel and steer the vehicle. Generally, the vehicle will travel in a direction perpendicular to the direction of tilt of the rotor assembly. Specifically, tilting the rotor assembly from side-to-side and fore-and-aft steers the vehicle in the forward/reverse and the left/right directions, respectively. It is also commonly understood that, in the case of a riding trowel having two rotor assemblies, the driven shafts of both rotor assemblies should be tiltable side-to-side for forward/reverse steering control, whereas only the driven shaft of one of the rotor assemblies needs to be tilted fore-and-aft for left/right steering control.
Many riding trowels are equipped with steering assemblies that are manually operated. Such systems are disclosed in applicant's co-pending patent application publication no. 2009/0028642 filed on Jan. 29, 2009 and titled “Concrete Trowel Steering System” as well as U.S. Pat. No. 4,046,484 to Holz and U.S. Pat. No. 5,108,220 to Allen et al. Such assemblies typically include two steering control handles mounted adjacent the operator's seat and accessible by the operator's left and right hands, respectively. Each lever is coupled, via a mechanical linkage assembly, to a pivotable gearbox of an associated rotor assembly. The operator steers the vehicle by tilting the levers fore-and-aft and side-to-side, thereby tilting the gearboxes side-to-side and fore-and-aft, respectively.
Manually operated steering control assemblies of the type disclosed in the Holz and Allen et al. patents are relatively difficult to operate because they require the imposition of a significant physical force by the operator both to move the handles to a particular position and to retain them in that position. Although the system disclosed in Patent Application Publication No. 2009/0028642 reduces the physical demands on the operator, such mechanical physical control of riding trowels can become fatiguing over the course of prolonged operation. To address these problems, trowels have been designed that are steered by powered actuators. For instance, applicant's prior U.S. Pat. No. 6,368,016 discloses a trowel that that is steered using electrically powered actuators to tilt the gearboxes. Still other power trowel steering systems are disclosed in U.S. Pat. Nos. 5,890,833, 6,053,660, and 6,592,290 to Allen and U.S. Pat. No. 5,816,740 to Multiquip. Each of the patents discloses a trowel that is steered by hydraulic actuators. Riding power steered finishing machines typically have one or more joysticks that are positioned proximate an operator seat. The joysticks generate instructions that are communicated to electronic or hydraulic actuators whose operation tilts the respective gearboxes to effect the steering operation. The actuators usually are energized proportionally to the direction and extent of joystick movement. Regardless of whether of the particular operating modality, for each joystick position, the actuator will tilt the gearbox a predetermined magnitude. Progressive changes in joystick tilting will commonly result in progressive changes in gearbox tilting. Because the operator input forces are very small, operator fatigue is significantly reduced during operation when compared to operation of traditional, mechanically steered machines.
Regardless if the steering system is electrical, mechanical, hydraulic, or a combination thereof, the response characteristics of the actuators of a riding power steered trowel are typically preset. These values commonly define the sensitivity and responsiveness of the steering system of the trowel to manipulations of the joystick. Typically, these values are factory preset. They set the extent of gearbox tilting for each of a full range of joystick positions. One system, proposed by the assignee and disclosed in European Application No. EP 1,586,723, additionally permits the response characteristics of an electrically steered trowel to be programmed in the field using a personal data assistant (PDA). Programming the trowel's controller requires intricate knowledge of electronic controls and of how to calibrate those controls. As a result, control calibration, adjustment, and/or fault detection functions are commonly performed by very well-trained personnel. Such configurations yield power steering equipped riding finishing trowels whose steering operation is generally fixed or preset after the fluid system is configured or after the controller is programmed. That is, the gearbox is tilted the same, predetermined amount for each joystick position under all operating conditions.
However, operator preference, as well as concrete and weather conditions, can affect the desired responsiveness of the steering system. Most notably, operators prefer a steering that can be “feathered” or have high resolution when maneuvering along the perimeter of a work area or around obstructions in the work area. Hence, they would prefer to operate the joysticks through a relatively large stroke with a relatively small response to maximize steerability. Conversely, when the machine is being operated over long straight stretches in the center of an unobstructed work area, they would prefer that the steering system respond more for given joystick stroke in order to maximize responsiveness. With respect to concrete conditions, the riding trowel becomes more responsive to steering inputs as the surface of the concrete cures. With respect to weather conditions, overcast, shaded, or otherwise protected concrete surfaces generally take longer to cure and are less susceptible to the drying effects of wind and sun, thereby effecting steering performance of the power trowel used for finishing such surfaces. In short, it is desirable for a variety of reasons to be able to adjust the response characteristics of a steering system of a trowel on the fly, i.e., while operating the trowel. Heretofore available power-steered riding trowels did not have this capability.
Accordingly, there is a need for a ride-on concrete finishing trowel having a power steering system that can be switched between two or more preset steering modes in which each steering mode incorporates a distinct steering association.